Flow rate sensor unit, flowmeter and flow sensor

ABSTRACT

A flow rate detector ( 5 ) including a heater and a temperature sensor is connected to a thermal conductor ( 6 ), and a fluid temperature detector ( 9 ) including a temperature sensor is connected to a thermal conductor ( 10 ). A housing ( 2 ) encloses the flow rate detector ( 5 ), the fluid temperature detector ( 9 ) and parts of thermal conductors ( 6, 10 ). The housing ( 2 ) also encloses a memory ( 1 ) that stores individual information of a flow rate sensor unit used for determining flow rates by using signals from a detector circuit containing the heater, the temperature sensor of the flow rate detector and the temperature sensor of the fluid temperature detector. The flow rate detector ( 5 ), the fluid temperature detector ( 9 ) and the memory ( 1 ) are connected to a plurality of leads ( 4 ) in the housing ( 2 ). The housing ( 2 ) is connected to a fluid channel ( 13 ), into which the thermal conductors ( 6, 10 ) extended. The flow rate sensor unit reduces the difference in measurment between the different sensor units.

TECHNICAL FIELD

The present invention relates to a fluid flow rate detecting technique,and particularly to a flowmeter for determining the flow rate orintegrated flow rate of fluid such as gas, liquid or the like and a flowrate sensor unit for use in the same, and a flow rate sensor fordetecting the flow rate of fluid flowing in a pipe.

BACKGROUND TECHNIQUE

There have been hitherto used various types of flow rate sensors (orflow velocity sensors) for determining the flow rate (or flow velocity)of various kinds of fluid, particularly liquid, and a so-called thermaltype (particularly, indirectly heated type) flow rate sensor has beenused because the price thereof can be reduced.

There is used an indirectly heated type flow rate sensor in which asensor chip having a thin film heater and a thin film temperature sensorlaminated on a substrate through an insulating film by using the thinfilm technique is disposed so that heat can be transferred between thesensor chip and fluid in a pipe. By supplying current to the heater, thetemperature sensor is heated to vary the electrical characteristic ofthe temperature sensor, for example, the value of the electricalresistance. The variation of electrical resistance value (based ontemperature increase of the temperature sensor) is varied in accordanceof the flow rate (flow velocity) of fluid flowing in the pipe. This isbecause a part of the heating value of the heater is transferred intothe fluid, the heating value dispersed into the fluid is varied inaccordance with the flow rate (flow velocity) of the fluid, and thus theheating value supplied to the temperature sensor is finally varied inaccordance with the flow rate (flow velocity) of the fluid, so that theelectrical resistance value of the temperature sensor is varied inaccordance with the flow rate (flow velocity) of the fluid. Thevariation of the electrical resistance value of the temperature sensoris also different in accordance with the temperature of the fluid, andthus a temperature sensor for temperature compensation is installed inan electrical circuit for detecting the variation of the electricalresistance value of the temperature sensor to suppress the variation ofthe flow rate measurement value due to the temperature of the fluid asmuch as possible.

For example, an indirectly heated type flow rate sensor using a thinfilm element disclosed in JP(A)-8-146026, which is estimated to beexcellent in thermal response, high in measurement precision, compact insize and low in cost, has the following construction.

That is, as shown in FIGS. 24A and 24B, a flow rate sensor 501 has athin film heater 503 and a thin film temperature sensor 504 which arelaminated on a substrate 502 through an insulating layer 505 by usingthe thin film technique, and it is used while disposed at a properposition of a pipe 506 as shown in FIG. 25.

In the flow rate sensor 501, the temperature sensor 504 is heated bysupplying current to the heater 503 to detect the variation of theelectrical resistance value of the temperature sensor 504. Since theflow rate sensor 501 is disposed in the pipe 506, a part of the heatingvalue of the heater 503 is dispersed through the substrate 502 to thefluid flowing in the pipe, and thus the heating value transferred to thetemperature sensor 504 corresponds to the value achieved by subtractingthe dispersed heating value from the heating value of the heater 503.Further, since the dispersed heating value is varied in accordance withthe flow rate of the fluid, the flow rate of the fluid flowing in thepipe 506 can be determined by detecting the variation of the electricalresistance value of the temperature sensor 504 which varies inaccordance with the heating amount being supplied thereto.

Furthermore, since the dispersed heating value is also varied inaccordance with temperature, a temperature sensor 507 is disposed at aproper position of the pipe 506 as shown in FIG. 25, and a temperaturecompensating circuit is added in the flow rate detecting circuit fordetecting the variation of the electrical resistance value of thetemperature sensor 504 to reduce the error of the flow rate measurementvalue due to the temperature of the fluid at maximum.

However, the conventional flow rate sensor 501 is directly mounted onthe metal pipe 506, and also the metal pipe 506 is exposed to theoutside air. Therefore, the heating value of fluid itself is dispersedto the outside air through the metal pipe having high thermalconductivity, or the heating value of the outside air is liable to besupplied to the fluid, resulting in reduction in the measurementprecision of the flow rate sensor 501. Particularly when the flow rateof fluid is very low, it has a great effect on the measurementprecision, and thus when the temperature difference between the fluidand the outside air is large or when the specific heat of the fluid issmall, the effect is more remarkable.

When the fluid is viscous fluid, particularly viscous fluid havingrelatively high-viscosity, particularly liquid, the flow velocity in thecross-section perpendicular to the flow direction of the fluid in thepipe 506 is largely different between the portion in the neighborhood ofthe pipe wall and the center portion, and the flow velocity vectorexhibits a substantially parabolic distribution having the extreme valueat the center portion. That is, the non-uniformity of the flow velocitydistribution is remarkable.

In the case where the substrate 502 or a casing 508 connected to thesubstrate 502 is merely mounted on the pipe wall and exposed to thefluid to detect the flow velocity at only the portion in theneighborhood of the pipe wall as described above, the flow velocitydistribution has a large effect on the precision of the flow ratemeasurement. This is because no consideration is given to the flowvelocity of fluid flowing at the central portion in the cross-section ofthe pipe and consideration is given to only the flow velocity of fluidflowing in the neighborhood of the pipe wall of the pipe. As describedabove, when the fluid is viscous fluid having relatively high viscosity,the conventional flow rate sensor has a problem that it is difficult toaccurately determine the flow rate. Even when the fluid has lowviscosity at normal temperature, the viscosity increases as thetemperature is reduced, so that the problem associated with the fluidviscosity as described above occurs. Particularly, the above problembased on the viscosity is more remarkable when the flow rate per unittime is relatively small than when the flow rate per unit time is large.

Further, the flow rate sensor 501 is used under various differentenvironments such as geographical conditions, indoors/outdoors, etc.,and various other factors such as season conditions, day/night, etc. arealso added particularly outdoors, so that consideration must be given totemperature variation due to external environments. However, theconventional flow rate sensor 501 is designed to be likely influenced bysuch external environmental temperature, so that the measurement valueof the flow rate has a large error. Therefore, a flow rate sensor thatcan determine the flow rate with high precision under broad externalenvironmental temperature has been required.

In order to solve this problem, a flow rate sensor as shown in FIG. 26has been proposed. This is substantially the same as disclosed inJP(A)-11-118566, for example.

In FIG. 26, a flow rate detector 306 having a thin film heater and athin film temperature sensor which are laminated on a substrate 302through an insulating layer is mounted on a horizontal portion 307 a ofa fin plate 307 which is bent in an L-shape, thereby forming a flow ratesensor 301. In a casing 308, glass 310 is sealingly filled between thevertical portion 307 b of the fin plate 307 and the opening portion of aflow pipe 309, and the flow rate detector 306 and the overall horizontalportion 307 a of the fin plate 307 are hermetically coated and fixed bysynthetic resin 311. The upper portion of the casing 308 is covered by alid 312.

Reduction in the measurement precision of the flow rate due to thedispersion of heating value to the outside air or supply of heatingvalue from the outside air, variation of flow rate in the lateralcross-section of the pipe, the effect of the external temperatureenvironment, etc. can be greatly overcome by the flow rate sensor 301described above.

However, in the above flow rate sensor 301, the flow rate detector 306and the synthetic resin 311 are directly brought into contact with eachother, so that the heating value owned by the temperature sensor flowsout to the synthetic resin 311 or the heating value flows from thesynthetic resin 311 into the temperature sensor. Further, the flow ratedetector 306 is joined to the horizontal portion 307 a of the fin plate307 by joint material 313 of silver paste having excellent thermalconductivity or the like, so that the heating value transferred throughthe fin plate 307 flows out to the synthetic resin 311 through the jointmaterial 313, or the heating value flows out from the synthetic resin311 to the fin plate 307. Accordingly, when the specific heat of thefluid is small or when the flow rate is low, the sensitivity of the flowrate sensor 301 may be reduced.

Besides, the glass 310 is filled between the vertical portion 307 b ofthe fin plate 307 and the opening portion of the flow pipe 309 tointercept the thermal transfer. However, when the fin plate is minutelyvibrated due to the fluid flow and the sealing state becomes imperfect,the heating value transferred through the fin plate 307 flows out to thecasing 308 through the metal flow pipe 309 having excellent thermalconductivity or the heating value flows from the casing 308 into the finplate 307. Accordingly, when the specific heat of the fluid is small orwhen the flow rate is low, the sensitivity of the flow rate sensor 301may be reduced as in the foregoing case.

The present invention has an object to solve the above problem andprovide a flow rate sensor that can suppress flow-in/flow-out of heatingvalue between each part of the flow rate sensor and a casing/theexternal to determine the flow rate with high precision even when thespecific heat of fluid is small, when the flow rate is low, etc., andcan be easily fabricated and reduced in cost.

The flow rate sensor disclosed in the above JP(A)-11-118566 uses anelectrical circuit containing a bridge circuit to achieve the electricaloutput corresponding to the flow rate of fluid.

In general, the output of the electrical circuit of the flow rate sensorhas no simple proportional relationship with the flow rate value.Therefore, in order to convert the output of the electrical circuit tothe flow rate value, data processing using a calibration curve may becarried out. The data processing is carried out by using amicrocomputer, and digital signals indicating the flow rate value may beinput to a display device or transmitted to a desired remote placethrough a communication line.

However, with respect to the flow rate sensor as described above, it isrequired to throw the contact portion thereof with fluid and thesurrounding portion thereof away periodically or after a predeterminedamount of fluid flows. For example, when the flow rate sensor is appliedto determine the flow rate of raw materials in a process of synthesizinghigh-purity reagent or medicines, throw-away is required from theviewpoint of surely preventing purity-reduction of products due tocontamination of impurities. Further, when it is applied to a flow ratemeasurement of samples in a chemical analysis such as chemical titrationor the like, throw-away is required from the viewpoint of preventing anadverse effect on the analysis due to unexpected chemical reactionsbecause the components contained in the samples are unknown. Stillfurther, when it is applied to a flow rate measurement of liquidmedicines being injected into a living body or a flow rate measurementof a body fluids picked up from a living body, throw-away is requiredfrom the viewpoint of preventing disease infection.

Actually, the throw-away portions have been strongly required to beminiaturized in size and reduced in cost. Therefore, it has beenconsidered to unify a thermal conductor to be extended into a fluidflowing pipe, a sensor chip fixed to the thermal conductor and wiresconnected to the terminals of the sensor chip into a unit as athrow-away portion.

However, in this case, the following problem occurs. That is, when asensor unit thus unified as described above is used as a disposableunit, a common calibration curve is used for plural sensor units in adata processing circuit to convert the output of the electrical circuitto the flow rate value. The calibration curve regulates-a standardrelationship, and no consideration is given to an individual conditionof each sensor. However, actually, the orientation of the thermalconductor to be extended to the external, the joint state between thesensor chip and the thermal conductor, the connection state between thesensor chip and the wires are minutely varied every sensor unit, andthus the relationship between the flow rate supporting output and theflow rate value is frequently varied every sensor unit. In this case, ameasurement error occurs in the flow rate measurement due to theindividual difference among sensor units, and thus the measurementprecision is reduced.

Therefore, an object of the present invention is to provide a flow ratesensor unit which can suppress occurrence of a flow rate measurementerror due to the individual difference of sensor units.

Further, another object of the present invention is to provide aflowmeter which can suppress occurrence of a flow rate measurement errordue to the individual difference of sensor units.

SUMMARY OF THE INVENTION

In order to attain the above objects, according to the presentinvention, there is provided a flow rate sensor unit in which a flowrate detector having a heater and a flow rate detecting temperaturesensor is joined to a flow rate detecting thermal conductor, and theflow rate detector and a part of the flow rate detecting thermalconductor are accommodated in a housing, characterized in that thehousing encloses a memory for storing individual information of the flowrate sensor unit used when a flow rate value is achieved on the basis ofa detection signal of a detecting circuit containing the heater and theflow rate detecting temperature sensor, and the flow rate detector andthe memory are connected to plural leads in the housing, the pluralleads being partially exposed to the outside of the housing.

In an aspect of the present invention, a fluid temperature detectorcontaining a fluid temperature detecting temperature sensor is joined toa fluid temperature detecting thermal conductor, the housing enclosesthe fluid temperature detector and a part of the fluid temperaturedetecting thermal conductor, the detecting circuit contains the fluidtemperature detecting temperature sensor, and in the housing the fluidtemperature detector is connected to plural leads which are partiallyexposed to the outside of the housing.

In an aspect of the present invention, the individual information storedin the memory is correction information for a standard calibration curveused when the flow rate value is achieved on the basis of the detectionsignal of the detecting circuit.

In an aspect of the present invention, a fluid channel is connected tothe housing, and the other part of the flow rate detecting thermalconductor extends into the fluid channel. In an aspect of the presentinvention, a fluid channel is connected to the housing, and the otherpart of the fluid temperature detecting thermal conductor extends intothe fluid channel.

In order to attain the above objects, according to the presentinvention, there is also provided a flowmeter including the above flowrate sensor unit and an electrical circuit portion connected to theleads of the flow rate sensor unit, wherein the electrical circuitportion achieves the fluid flow rate value on the basis of the detectionsignal of the detecting circuit by referring to a standard calibrationcurve stored in advance, and at that time corrects the standardcalibration curve by using the individual information stored in thememory of the flow rate sensor unit.

In an aspect of the present invention, the electrical circuit portionincludes an analog circuit portion for achieving the outputcorresponding to the flow rate of the fluid by using the detectionsignal of the detecting circuit, and a digital circuit portion forachieving the fluid flow rate value on the basis of the output of theanalog circuit, and the digital circuit portion includes a microcomputerand a main memory for storing the standard calibration curve.

In an aspect of the present invention, the individual information storedin the memory of the flow rate sensor unit reflects plural relationshipsbetween the output value corresponding to the fluid flow rateactually-measured for the flow rate sensor unit and the true fluid flowrate value.

In an aspect of the present invention, the leads of the flow rate sensorunit and the electrical circuit portion are detachably connected to eachother.

In order to attain the above objects, according to the presentinvention, there is also provided a flow rate sensor unit in which aflow rate detector having a heater and a flow rate detecting temperaturesensor is joined to a flow rate detecting thermal conductor, and theflow rate detector and a part of the flow rate detecting thermalconductor are accommodated in a housing, characterized in that a fluidchannel is connected to the housing, the other part of the flow ratedetecting thermal conductor extends into the fluid channel, a thermalconductor extending from the inside of the housing into the fluidchannel is disposed, the housing encloses a memory for storingindividual information of the flow rate sensor unit used when a flowrate value is achieved on the basis of a detection signal of a detectingcircuit containing the heater and the flow rate detecting temperaturesensor, and the flow rate detector and the memory are connected toplural leads in the housing, the plural leads being partially exposed tothe outside of the housing.

In an aspect of the present invention, a fluid temperature detectorcontaining a fluid temperature detecting temperature sensor is joined toa fluid temperature detecting thermal conductor, the housing enclosesthe fluid temperature detector and a part of the fluid temperaturedetecting thermal conductor, the other part of the fluid temperaturedetecting thermal conductor extends into the fluid channel, thedetecting circuit contains the fluid temperature detecting temperaturesensor, and in the housing the fluid temperature detector is connectedto plural leads which are partially exposed to the outside of thehousing.

In an aspect of the present invention, the individual information storedin the memory is correction information for a standard calibration curveused when the flow rate value is achieved by using the detection signalof the detecting circuit.

In an aspect of the present invention, the thermal conductor extends tobe nearer to the portions of the leads in the housing than the flow ratedetecting thermal conductor. In an aspect of the present invention, thethermal conductor extends to be nearer to the portions of the leads inthe housing than the fluid temperature detecting thermal conductor.

In an aspect of the present invention, the memory is joined to thethermal conductor.

In an aspect of the present invention, the flow rate detecting thermalconductor, the fluid temperature detecting thermal conductor and thethermal conductor are designed in a plate shape, and arranged along thedirection of the fluid channel on the same plane in the fluid channel.

In order to attain the above objects, according to the presentinvention, there is also provided a flowmeter containing the above flowrate sensor unit and an electrical circuit portion connected to theleads of the flow rate sensor unit, wherein the electrical circuitportion achieves the fluid flow rate value on the basis of the detectionsignal of the detecting circuit by referring to a standard calibrationcurve stored in advance, and at that time corrects the standardcalibration curve by using the individual information stored in thememory of the flow rate sensor unit.

In an aspect of the present invention, the electrical circuit portionincludes an analog circuit portion for achieving the outputcorresponding to the flow rate of the fluid by using the detectionsignal of the detecting circuit, and a digital circuit portion forachieving the fluid flow rate value on the basis of the output of theanalog circuit, and the digital circuit portion includes a microcomputerand a main memory for storing the standard calibration curve.

In an aspect of the present invention, the individual information storedin the memory of the flow rate sensor unit reflects plural relationshipsbetween the output value corresponding to the fluid flow rateactually-measured for the flow rate sensor unit and the true fluid flowrate value.

In an aspect of the present invention, the leads of the flow rate sensorunit and the electrical circuit portion are detachably connected to eachother.

In order to attain the above objects, according to the presentinvention, there is also provided a flow rate sensor comprising a flowrate measuring portion for detecting the flow rate of fluid, atemperature compensating measuring portion for compensating an effect offluid temperature on measurements of the flow rate measuring portion,and a housing, wherein the flow rate measuring portion includes a flowrate detector having a heater and a temperature sensor laminated eachother through an insulator, a fin plate joined to the flow rate detectorat one end thereof, and an output terminal electrically connected to theflow rate detector, the temperature compensating measuring portionincludes a temperature detector having an insulator and a temperaturesensor that are laminated on each other, a fin plate joined to thetemperature detector at one end thereof, and an output terminalelectrically connected to the temperature detector, the housing enclosesthe flow rate detector and the temperature detector therein, and the finplates and the output terminals of the flow rate measuring portion andthe temperature compensating measuring portion are projected to theoutside of the housing.

The housing is preferably formed of synthetic resin having thermalconductivity of 0.7 W/m·K or less. In the flow rate sensor according tothe present invention, it is preferable that a cavity portion isprovided in the housing, and the flow rate detector and the temperaturedetector are mounted at a position of the cavity portion at which theflow rate detector and the temperature detector are not brought intocontact with the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a flow rate sensorunit according to the present invention;

FIG. 2 is a cross-sectional view taken along A—A′ of FIG. 1;

FIG. 3 is an exploded perspective view showing the construction of aflow rate detector;

FIG. 4 is an exploded perspective view showing the construction of afluid temperature detector;

FIG. 5 is a schematic cross-sectional view showing a flow rate sensorunit according to the present invention;

FIG. 6 is a cross-sectional view taken along A—A′ of FIG. 5;

FIG. 7 is a schematic diagram showing a flowmeter of the presentinvention;

FIG. 8 is a diagram showing an example of the connection between a flowrate sensor unit and an electrical circuit portion of the flowmeteraccording to the present invention;

FIG. 9 is a circuit diagram showing the flowmeter according to thepresent invention;

FIG. 10 is a diagram showing an example of a calibration curve in theflowmeter of the present invention;

FIG. 11 is a diagram showings standard calibration curve and a correctedcalibration curve in the flowmeter of the present invention;

FIG. 12 is a schematic cross-sectional view showing a flow rate sensorunit according to the present invention;

FIG. 13 is a cross-sectional view taken along A—A′ of FIG. 12;

FIG. 14 is a schematic cross-sectional view showing a flow rate sensorunit according to the present invention;

FIG. 15 is a cross-sectional view taken along A—A′ of FIG. 14;

FIG. 16 is a diagram showing an example of the connection between theflow rate sensor unit and the electrical circuit portion in theflowmeter of the present invention;

FIG. 17 is a perspective view showing an embodiment of a flow ratesensor of the present invention;

FIGS. 18A and 18B are longitudinally-sectional views showing the.embodiment of the flow rate sensor of the present invention;

FIGS. 19A and 19B are longitudinally-sectional views showing anotherembodiment of the flow rate sensor according to the present invention;

FIG. 20 is a diagram showing a method of manufacturing the flow ratesensor;

FIG. 21 is a longitudinally-sectional view showing an embodiment of aflow rate detecting apparatus in which the flow rate sensor is fitted;

FIG. 22 is a longitudinally-sectional view showing the flow ratedetecting apparatus from which the flow rate sensor is removed;

FIG. 23 is an electrical circuit diagram showing the flow rate detectingapparatus;

FIG. 24A is a perspective view showing a conventional flow rate sensor;

FIG. 24B is a longitudinally-sectional view of the flow rate sensor ofFIG. 24A;

FIG. 25 is a cross-sectional view showing the state that theconventional flow rate sensor is disposed in a pipe; and

FIG. 26 is a diagram showing the flow rate sensor and the flow ratedetecting apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments according to the present invention will bedescribed with reference to the accompanying drawings.

FIG. 1 is a schematic cross-sectional view showing an embodiment of aflow rate sensor unit according to the present invention, and FIG. 2 isa cross-sectional view taken along A—A′ of FIG. 1.

As is shown in FIGS. 1 and 2, a flow rate detector 5 is joined on thesurface of a fin plate 6 serving as a flow rate detecting thermalconductor, and a fluid temperature detector 9 is joined on the surfaceof a fin plate 10 serving as a fluid temperature detecting thermalconductor. The flow rate detector 5, the fluid temperature detector 9and a part of each of the fin plates 6, 10 are accommodated in a housing2.

As shown in FIG. 3, the flow rate detector 5 is designed in the form ofa chip by laminating a flow rate detecting thin film temperature sensor31, an interlayer insulating film 32, a thin film heater 33, electrodes34, 35 for the heater and a protection film 36 in this order on arectangular substrate 30 of about 0.4 mm in thickness and about 2 mm insquare which is formed of silicon or alumina, for example, and thenforming a pad layer 37 coated on the bonding portion of the flow ratedetecting thin film temperature sensor 31 and the heater electrodes 34,35.

The thin film temperature sensor 31 may be a metal resistance film ofplatinum (Pt) or nickel (Ni) having a large and stable temperaturecoefficient which is patterned in a desired form, for example in ameandering form so as to have a film thickness of about 0.5 to 1μm.Alternatively, it may be an NTC thermistor of manganese oxide group. Theinterlayer insulating film 32 and the protection film 36 may be formedof SiO₂ at a thickness of about 1μm, for example. The thin film heater33 may comprise a resistor of Ni, Ni—Cr, Pt, or cermet such as Ta—SiO₂,Nb—SiO₂ or the like, which is patterned to have a desired shape and afilm thickness of about 1μm. The heater electrodes 34, 35 may be formedof an Ni layer having a thickness of about 1μm or a laminate of the Nilayer and a gold (Au) layer of 0.5μm laminated thereon. The pad layer 37may be formed of an Au thin film or Pt thin film having a thickness ofabout 0.1 μm and a size of 0.2 mm×0.15 mm in longitudinal and lateraldirections.

As shown in FIG. 4 the fluid temperature detector 9 has the sameconstruction as the flow rate detector 5 except that the thin filmheater 33, etc. are removed from the flow rate detector 5, that is, itis designed in a chip form by laminating a fluid temperature detectingthin film temperature sensor 31′ having the same construction as thethin film temperature sensor 31 and a protection film 36′ having thesame construction as the protection film 36 in this order on a substrate30′ having the same construction as the substrate 30, and then forming apad layer 37′ so as to cover the bonding portion of the fluidtemperature detecting thin film temperature sensor 31′.

One surfaces of one end portions of the fin plates 6, 10 are joined tothe surfaces of the substrates 30, 30′ of the flow rate detector and thefluid temperature detector 9 by joint material having excellent thermalconductivity. The fin plate 6, 10 may be a rectangular plate of about0.2 mm in thickness and about 2 mm in width, which is formed of, copper,duralumin, copper-tungsten alloy or the like. Silver paste may be usedas the joint material.

As shown in FIGS. 1 and 2, a fluid channel member 12 is connected to thehousing 2 of a sensor unit, and the other end portions of the fin plates6, 10 extend into a fluid channel 13 formed in the fluid channel member12. The fin plates 6, 10 extend in the fluid channel 13 having thesubstantially circular cross-section so as to pass through the center ofthe cross-section of the fluid channel 13. The fin plates 6, 10 aredisposed along the fluid flowing direction (indicated by an arrow ofFIG. 1) in the fluid channel 13. Therefore, they can excellently performthermal transfer (thermal conduction) between the fluid and each of theflow rate detector 5 and the fluid temperature detector 9 withoutsignificantly disturbing the flow of fluid in the fluid channel 13.

The housing 2 and the fluid channel member 12 may be formed of syntheticresin such as epoxy resin, polyphenylene sulfide resin or the like. Achip-shaped semiconductor memory 1 for storing individual information ofthe sensor unit is accommodated in the housing 2. The individualinformation stored in the memory 1 will be described later.

Each electrode terminal (pad) of the flow rate detector 5, the fluidtemperature detector 9 and the memory 1 is connected to the inner leadportion (each portion in the housing) 4 a of each lead 4 by an Au wire3. Each lead 4 extends to the outside of the housing 2 and is partiallyexposed to the outside of the housing to thereby form an outer leadportion 4 b. The outer lead portion 4 b may be of a J-bent type, forexample.

In FIGS. 1 and 2, a space 15 is formed at the center portion of thehousing 2, and the detectors 5, 9, parts of the fin plates 6, 10 and theinner lead portions 4 a are located in the space 15. Actually, as shownin FIG. 2, the space 15 is covered by a cover 16 which is formedintegrally with the housing 2, or sealed with synthetic resin so that itis integrated with the housing 2.

A modification of the flow rate sensor unit thus constructed will bedescribed with reference to FIGS. 5 and 6. In FIGS. 5 and 6, the membersand portions having the same functions as those of FIGS. 1 and 2 arerepresented by the same reference numerals. This modification isdifferent from the construction shown in FIGS. 1 and 2 only in that thehousing 2 is formed integrally with the fluid channel member 12 in thesame molding process.

Next, FIG. 7 shows an embodiment of a flowmeter using the flow sensorunit as described above.

A socket 20 is fitted to the outer lead portions 4 b exposed to theoutside of the housing 2 of the sensor unit, and wires 21 are connectedto the socket 20. Each of the wires is electrically connected to eachouter lead portion 4 b at one end thereof, and also connected to anelectrical circuit portion 22 at the other end thereof. The electricalcircuit portion 22 has an analog circuit portion 23, a digital circuitportion 24 and a display portion 25, the wires 21 are connected to theanalog circuit portion 23, and the output of the analog circuit portion23 is input to the digital circuit portion 24. The digital circuitportion 24 is connected to the display portion 25 and a communicationline for communications with the external.

FIG. 8 shows a modification of the connection between the flow ratesensor unit as described above and the electrical circuit portion. Inthis modification, a modular jack 26 is interposed at some midpoint ofthe wires 21, and the wires 21 can be separated into the sensor unitside wiring portion 21 a and the electrical circuit side wiring portion21 b by the modular jack 26. Accordingly, the wiring portion 21 a, thesocket 20 and the flow rate sensor unit secured to the socket can beremoved from the wiring portion 21 b by the modular jack 26 whilekeeping the connection between the housing 2 and the socket 20.Accordingly, the wiring portion 21 a and the socket 20 can be discardedtogether with the flow rate sensor unit. This construction increases thenumber of parts to be thrown away, however, there is avoided thevariation imposed on the extension state of the fin plates 6, 10 intothe fluid channel in such a case that the housing 2 is mounted onto thesocket 20, and thus the attaching/detaching operation can be easilyperformed.

FIG. 9 is a circuit diagram of the above flowmeter.

AC 100V is used as a power supply source, and DC voltages of +15V, −15V,+5V generated from AC 100V are output by a DC converting circuit 71. TheDC voltage of +15V output from the DC converting circuit 71 is input toa voltage stabilizing circuit 72.

The stabilized DC voltage supplied from the voltage stabilizing circuit72 is supplied to a bridge circuit (detection circuit) 73. The bridgecircuit 73 comprises a flow rate detecting temperature sensor 31, atemperature compensating temperature sensor 31′, a resistor 74 and avariable resistor 75. The potentials Va, Vb at a, b points of the bridgecircuit 73 are input to a differential amplifying circuit 76 havingvariable amplification factor. The output of the differential amplifyingcircuit 76 is input to an integrating circuit 77.

The output of the voltage stabilizing circuit 72 is supplied to a thinfilm heater 33 through an electric field effect transistor 81 forcontrolling the current supplied to the thin film heater 33. That is, inthe flow rate detector 5, on the basis of the heating of the thin filmheater 33, the temperature sensing operation of the thin filmtemperature sensor 31 is carried out while suffering an effect ofendothermic action of fluid to be examined through the fin plate 6. As aresult of the temperature sensing, the difference between the potentialsVa, Vb at the a, b points of the bridge circuit 73 shown in FIG. 9 isachieved.

The temperature of the flow rate detecting temperature sensor 31 isvaried in accordance with the flow rate of fluid, and the variation ofthe temperature of the flow rate detecting temperature sensor 31 causesvariation of the value (Va−Vb). By setting the resistance value of thevariable resistor 75 to a proper value in advance, the value of (Va−Vb)can be set to zero when the flow rate of the fluid is equal to a desiredvalue (reference value). At this reference flow rate, the output of thedifferential amplifying circuit 76 is equal to zero, and the output ofthe integrating circuit 77 is equal to a fixed value (the valuecorresponding to the reference flow rate). The output of the integratingcircuit 77 is subjected to level adjustment so that the minimum value isequal to 0V.

The output of the integrating circuit 77 is input to a V/F convertingcircuit 78, in which a pulse signal having the frequency (for example,5×10⁻⁵ at maximum) corresponding to a voltage signal is formed. Thepulse signal has a fixed pulse width (time interval) (for example, adesired value in the range from 1 to 10 μsec). For example, when theoutput of the integrating circuit 77 is equal to 1V, a pulse signalhaving a frequency of 0.5 kHz is output, and when the output of theintegrating circuit 77 is equal to 4V, a pulse signal having a frequencyof 2 kHz is output.

The output of the V/F converting circuit 77 is supplied to the gate ofthe transistor 81. Current flows into the thin film heater 33 throughthe transistor whose gate is supplied with the pulse signal.Accordingly, a divided voltage of the output voltage of the voltagestabilizing circuit 72 is applied to the thin film heater 33 through thetransistor at the frequency corresponding to the output value of theintegrating circuit 77 and in the pulse form, whereby currentintermittently flows into the thin film heater 33 to heat the thin filmheater 33. The frequency of the V/F converting circuit 77 is set on thebasis of a high-precision clock which is set on the basis of oscillationof a temperature compensated type quartz oscillator 79 in a referencefrequency generating circuit 80.

The analog circuit portion 23 is constructed to contain the aboveelements.

The pulse signal output from the V/F converting circuit 77 is counted bya pulse counter 82. On the basis of the result (pulse frequency) of thepulse counting which is carried out on the basis of the frequencygenerated in the reference frequency generating circuit 80, amicrocomputer 83 converts the result to the corresponding flow rate(instantaneous flow rate), and integrates the flow rate thus achievedwith respect to time to thereby calculate an integrated flow rate.

The conversion to the flow rate is carried out by using a standardcalibration curve stored in the main memory 84 in advance. FIG. 10 showsan example of the calibration curve. That is, a data table achieved bymeasuring the pulse frequency output from the pulse counter 82 everyflow rate of fluid by using a flow rate sensor unit as a referencesensor unit is stored as a standard calibration curve in the main memory84.

In this embodiment, individual information of a sensor unit for flowrate measurements is stored in the memory 1 of the sensor unitconcerned. The individual information is data indicating pluralcorresponding relationships between the true flow rate value and theoutput pulse frequency of the pulse counter 82 achieved in advance byactually measuring the flow rate with the sensor unit concerned.

The individual information will be described with reference to FIG. 11.A standard calibration curve SL is shown in FIG. 11. The standardcalibration curve SL shows the relationship between a flow rate value xand a pulse frequency value y. The relationship of (flow ratevalue−pulse frequency value) at points P, Q in FIG. 11, that is, P(x₁,Y₁) and Q(x₂, Y₂) are stored in the built-in memory 1 of the sensorunit.

The data storage into the memory 1 as described above may be carried outas follows. That is, EEPROM is used as the memory 1, under the existenceof the space 15 as shown in FIGS. 1 and 2 (that is, before the resinsealing and provision of the cover 16), fluid is made flow at flow ratevalues of x₁ and x₂ to measure the output pulse frequency values y₁ andY₂, and these measurement values are written into EEPROM by laserirradiation. After the individual information is stored into the memory1 as described above, the space 15 is sealed with resin or the cover 16is mounted on the space 15, thereby completing the sensor unit. Withthis process, the sensor unit containing the memory 1 can bemanufactured in low cost. The memory 1 of the present invention is notlimited to EEPROM, and different kinds of writable memories may be used.

In the microcomputer 83, when the flow rate of fluid to be examined ismeasured, the standard calibration curve is first corrected on the basisof the individual information as described above to create a correctedcalibration curve. That is, a corrected calibration curve CL passingthrough (x₁, y₁) and (x₁, Y₂) is achieved on the basis of the standardcalibration curve SL as shown in FIG. 11 and the individual informationP(x₁, y₁) and Q (x₂, Y₂). Specifically, when the pulse frequency valueis equal to y₁, the corrected flow rate value is set to the sum of theflow rate value x and the correction value [containing sign] C(y₁),i.e., [x+C(y₁)]. When the pulse frequency value is equal to y₂, thecorrected flow rate value is set to the sum of the flow rate value x andthe correction value [containing sign] C(y₂), that is, [x+C(y₂)]. In thecase of the other pulse frequency values y, the correction value C(y)may be set by the extrapolating or interpolating method, for example. Atthis time, a function form of y=f(x) for the standard calibration curveSL is considered, and the extrapolation or interpolation is carried outso that the displacement from this function form is as less as possible.

In the foregoing description, the individual information comprises twopoints P(x₁, y₁) and Q(x₂, Y₂), however, the corrected calibration curveCL can be further easily achieved by setting the individual informationto three or more points.

As described above, the microcomputer 83 specifies as a measurementvalue the corrected flow rate value on the corrected calibration curveCL corresponding to the pulse frequency output from the pulse counter 82when the flow rate measurement is carried out (the reference flow ratevalue may be achieved by using the standard calibration curve and thenadded with the correction value C(y) as described above).

The digital circuit portion 30 is constructed by containing the aboveelements.

The values of the instantaneous flow rate and the integrated flow ratethus achieved are displayed on the display portion 25, and alsotransmitted to the external through a communication line such as atelephone line or other network. If necessary, the data of theinstantaneous flow rate and the integrated flow rate may be stored inthe main memory 84.

Reference numeral 85 represents a backup power source (for example,battery).

If the flow rate increases/decreases, the polarity (which is differentin accordance with the positive/negative sign of theresistance-temperature characteristic of the flow rate detectingtemperature sensor 31) and magnitude of the output of the differentialamplifying circuit 76 is varied in accordance with the value of (Va−Vb),and the output of the integrating circuit 77 is also varied inaccordance with the above variation. The variation velocity of theoutput of the integrating circuit 77 may be adjusted by setting theamplification factor of the differential amplifying circuit 76. Theresponse characteristic of the control system is set by the integratingcircuit 77 and the differential amplifying circuit 76.

When the flow rate of fluid is increased, the temperature of the flowrate detecting temperature sensor 31 is reduced. Therefore, such anoutput (a higher voltage value) of the integrating circuit 77 asincreases the heating value of the thin film heater 33 (that is,increases the pulse frequency) is achieved, and the bridge circuit 73 isset to an equilibrium state at the time point when the output of theintegrating circuit is equal to the voltage corresponding to the flowrate of the fluid.

On the other hand, when the fluid flow rate is reduced, the temperatureof the flow rate detecting temperature sensor 31 increases, so that suchan output (a lower voltage value) of the integrating circuit 77 asreduces the heating value of the thin film heater 33 (that is, reducesthe pulse frequency) is achieved, and the bridge circuit 73 is set tothe equilibrium state at the time point when the output of theintegrating circuit is equal to the voltage corresponding to the fluidflow rate.

That is, in the control system of this embodiment, the frequency of thepulse-shaped current (corresponding to the heating value) to be suppliedto the thin film heater 33 is set so that the bridge circuit 73 is setto the equilibrium state, and such an equilibrium state as describedabove (response of the control system) can be realized within 0.1second, for example.

In the above-described embodiment, the standard calibration curve iscorrected on the basis of the individual information of a newly usedflow rate sensor unit. Therefore, even when the joint state between thechip of each of the flow rate detector 5 and the fluid temperaturedetector 9 and the corresponding thermal conductor, the wire bondingconnection state between the chip of each of the flow rate detector 5and the fluid temperature detector 9 and the leads, etc. are differentamong individual flow rate sensor, the flow rate measurement can beperformed with high precision by each flow rate sensor unit.Accordingly, even when the electrical circuit portion of the flowmeteris continuously used and the flow rate sensor unit is thrown away, thehigh measurement precision can be kept, and the field to which the flowrate measurement is applied can be enlarged.

Further, according to the above-described embodiment, the pulse signalgenerated by the V/F converting circuit 78 is used, and the error due totemperature variation can be sufficiently reduced for the pulse signal,and thus the error of the flow rate value and the integrated flow ratevalue achieved on the basis of the pulse frequency can be reduced. Inaddition, according to this embodiment, the control of current to besupplied to the thin film heater 33 is carried out on the basis of theON-OFF operation based on the pulse signal generated in the V/Fconverting circuit 78, so that a control error due to temperaturevariation occurs with extremely small probability.

Still further, according to this embodiment, a minute chip containing athin film heater and a thin film temperature sensor is used as a flowrate detector, so that high-speed response can be implemented and theprecision of the flow rate measurement can be enhanced.

Still further, according to this embodiment, irrespective of the flowrate of the fluid to be examined, the temperature of the flow ratedetecting temperature sensor 31 around the thin film heater 33 is set toa substantially constant value, so that deterioration of the flow ratesensor unit with time can be suppressed and occurrence of ignitionexplosion of combustible fluid to be examined can be prevented.

FIG. 12 is a schematic cross-sectional view showing an embodiment of aflow rate sensor unit according to the present invention, and FIG. 13 isa cross-sectional view taken along A—A′ of FIG. 12. In FIGS. 12 and 13,the members and portions having the same functions as those of FIGS. 1and 2 are represented by the same reference numerals. This embodiment issubstantially different from the embodiment of FIGS. 1 and 2 in that finplates 17, 18 serving as a thermal conductor are disposed. The finplates 17, 18 are partially accommodated in the housing 2. The flow ratedetector 5 is designed in the form of a chip as shown in FIG. 3. Thefluid temperature detector 9 is designed in the form of a chip as shownin FIG. 4.

As shown in FIGS. 1 and 2, the fluid channel member 12 is connected tothe housing 2 of the sensor unit, and the end portions of the fin plates6, 10, 17, 18 extend to the inside of the fluid channel 13 formed in thefluid channel member 12. The fin plates 6, 10, 17, 18 extend in thefluid channel 13 having a substantially circular cross-section so as topass the center of the cross-section of the fluid channel 13. Since thefin plates 6, 10, 17, 18 are arranged along the fluid flowing direction(indicated by an arrow of FIG. 12) in the fluid channel 13, the thermalconduction through the fin plates 6, 10 between each of the flow ratedetector 5 and the fluid temperature detector 9 and the fluid and thethermal conduction through the fin plates 17, 18 between the inside ofthe housing and the fluid can be excellently performed.

The fin plates 17, 18 may be formed of the same material as the finplates 6, 10, and the fin plates 17, 18 can be formed together with thefin plates 6, 10 and the leads 4 by patterning a plate-shaped member.The fin plate 17 is formed so as to extend to the gap between the innerlead portion 4 a and the flow rate detector 5 in the housing 2, that is,it extends to a position nearer to the inner lead portion 4 a than theflow rate detector 5. Likewise, the fin plate 18 is formed so as toextend to the gap between the inner lead portion 4 a and the fluidtemperature detector 9 in the housing 2, that is, it extends to aposition nearer to the inner lead portion 4 a than the fluid temperaturedetector 9.

The wires 3 are arranged so as to stride over the end portions of thefin plates 17, 18 in the housing, so that insulating films 17′, 18′ canbe formed on the end portions of the fin plates 17, 18 to avoid thecontact between the wires 3 and the fin plates 17, 18. However, when thewires 3 are formed so as to extinguish the probability that the wires 3come into contact with the fin plates 17, 18, the insulating films 17′,18′ may be omitted.

By arranging the fin plates 17, 18, the thermal conduction between thefluid flowing in the fluid channel 13 and the inside of the housing 2(particularly, the areas between the inner lead portion 4 a and the flowrate detector 5 and between the inner lead portion 4 a and the fluidtemperature detector 9) can be excellently performed, and even when heatflow occurs between the inside and the outside of the housing 2 throughthe leads 4, the flow rate detector 5 and the fluid temperature detector9 can be effectively prevented from being influenced by the heat flow.Particularly, heat flowing into the housing 2 through the leads 4 can beeffectively leaked to the fluid in the fluid channel 13.

A modification of the flow rate sensor unit as described above is shownin FIGS. 14 and 15. In FIGS. 14 and 15, the members and portions havingthe same functions as those of FIGS. 12 and 13 are represented by thesame reference numerals. In this modification, the fin plate 19 servingas a thermal conductor is disposed at the intermediate position betweenthe fin plates 6, 10. The memory 1 is connected to the end portion ofthe fin plate 19 located in the housing.

The inner lead portion 4 a is located at a distance of L1 from the endportions of the fin plates 6, 10 located in the housing, and thedistance L2, L3 between the inner lead portion 4 a and the end portionof the fin plate 19 located in the housing is set to a distance smallerthan L1. For example, the distance L1 is set to 3mm or more, and thedistances L2, L3 are set to a value less than 3mm.

By disposing the fin plate 19, the thermal conduction between the fluidflowing in the fluid channel 13 and the inside of the housing 2(particularly, an area in the neighborhood of the inner lead portion 4a) is excellently performed, and even when heat flow occurs between theinside and the outside of the housing 2 through the leads 4, the flowrate detector 5 and the fluid temperature detector 9 can be effectivelyprevented from being influenced by the heat flow.

In the embodiment and the modification described above, the housing 2and the fluid channel member 12 can be integrally formed with each otherin the same molding process.

A flowmeter can be constructed by using the flow rate sensor unit asdescribed above in the same manner as described with reference to FIG.7. FIG. 16 shows a modification of the connection between the flow ratesensor unit as described above and the electrical circuit portion. Thismodification has the same connection as shown in FIG. 8 except that theflow rate sensor unit having the fin plates 17, 18 is used. Thisarrangement can suppress variation imposed on the extension state of thefin plates 6, 10, 17, 18 in the fluid channel in such a case that thehousing 2 is mounted onto the socket 20, so that the attaching/detachingoperation can be easily performed.

The circuit construction of the flowmeter as described above is the sameas described with reference to FIG. 9. The standard calibration curvewhich is used for the conversion to the flow rate in the flowmeter andstored in the main memory 84 in advance is the same as described withreference to FIG. 10. Further, the recording operation of the individualinformation of the sensor unit into the memory 1 of the sensor unitconcerned and the flow rate measuring process of the fluid to beexamined which is carried out in the microcomputer 83 by using theindividual information are the same as described on the embodiment ofFIGS. 1 and 2 with reference to FIG. 11.

Next, an embodiment of a flow rate sensor according to the presentinvention will be described.

FIG. 17 is a perspective view showing an embodiment of a flow ratesensor according to the present invention. FIG. 18A is alongitudinally-sectional view showing the flow rate sensor of FIG. 17,and FIG. 18B is a longitudinally-sectional view taken along X—X line ofFIG. 18A.

As shown in FIGS. 17, 18A and 18B, a flow rate sensor 101 comprises ahousing 102, a flow rate measuring portion 103 and a temperaturecompensating measuring portion 104.

As shown in FIGS. 18A and 18B, the flow rate measuring portion 103comprises a flow rate detector 105 mounted in the housing 102, a finplate 106 which is joined to the flow rate detector 105 at one endthereof and extends to the outside of the housing 102 at the other endthereof, and bonding wires 108 for electrically connecting the flow ratedetector 105 to output terminals 107 each of which is joined to eachbonding wire 108 at one end thereof and extends to the outside of thehousing 102 at the other end thereof.

The temperature compensating measuring portion 104 comprises atemperature detector 109 mounted in the housing 102, a fin plate 110which is joined to the flow rate detector 109 at one end thereof andextends to the outside of the housing 102 at the other end thereof; andbonding wires 112 for electrically connecting the temperature detector109 to output terminals Ill each of which is joined to each bonding wire112 at one end thereof and extends to the outside of the housing 102 atthe other end thereof.

The flow rate sensor shown in FIGS. 18A and 18B has such a structurethat no cavity portion is provided in the housing 102 and thesurrounding portion of the flow rate detector 105 and the temperaturedetector 109 are filled with resin. In this case, in order to suppressthe thermal transfer between each part of the flow rate sensor and acasing serving as a peripheral structure of the flow rate sensor atmaximum, it is necessary to use synthetic resin having small thermalconductivity as the material of the housing 102. Specifically, if thethermal conductivity is set to 0.7 W/m·K or less, preferably 0.4 W/m·Kor less, the heat conduction amount in the housing 102 can be reducedand thus the flow rate can be measured with high precision.

FIGS. 19A and 19B show another embodiment of the flow rate sensor of thepresent invention. In this embodiment, a cavity portion is provided inthe housing. FIG. 19A is a longitudinally-sectional view of the flowrate sensor, and FIG. 19B is a longitudinally-sectional view taken alongX—X line of FIG. 19A.

In FIGS. 19A and 19B, the flow rate sensor 121 is disposed in the cavityportion 123 of the housing 122 so that both of the flow rate detector105 of the flow rate measuring portion 103 and the temperature detector109 of the temperature compensating measuring portion 104 are notbrought into contact with the resin forming the housing 122. The outputterminals 107, 111 are fixed to the wall of the housing 122.

By providing the cavity portion 123 in the housing 122 as shown in FIGS.19A and 19B, even when the thermal conductivity of the resin forming thehousing 122 is relatively large, the thermal transfer between each partof the flow rate sensor and the structure (casing) surrounding the flowrate sensor can be suppressed at maximum by the adiabatic effect of thecavity portion 123.

If a notch portion is formed on the outer peripheral surface of the flowrate sensor so that an adiabatic gap occurs between the flow rate sensorand the casing, heat transfer between the flow rate sensor and thecasing can be effectively suppressed.

Next, each part of the flow rate sensor will be described (see FIGS. 18Aand 18B).

The housing 102 is preferably formed of rigid resin having high chemicalresistance and high oil resistance, and more preferably formed of resinhaving low thermal conductivity such as epoxy resin, polybutyleneterephthalate (PBT), polyphenylene sulfide (PPS) or the like.

The output terminals 107, 111 are linear thin plates of about 200 μm inthickness which are formed of material having high conductivity such ascopper or the like.

It is preferable that the output terminals 107, 111 are juxtaposed withone another on a line so as to project to the outside of the resinhousing 102 and so that the projection length thereof from the resinhousing 102 is gradually increased (reduced) from one end of the linearline to the other end thereof. This construction facilitates themounting work of a sensor press plate for pressing the flow rate sensor101 from the upper side and a flow rate detecting circuit board which isconnected to the output terminals 107, 111 to form a circuit, and alsoreduces such a risk that the flow rate sensor 101 is damaged when thesensor press plate or the flow rate detecting circuit board is mounted.

The end portions of the output terminals 107, 111 located in the housingare assembled so as to be proximate to one another, thereby facilitatingthe work of connecting the bonding wires 108, 112 to the outputterminals 107, 111, the flow rate detector 105 and the temperaturedetector 109.

Each of the fin plates 106, 110 comprises a rectangular thin plate ofabout 200 μm in thickness and about 2mm in width which is formed ofmaterial having high thermal conductivity such as copper, duralumin,copper-tungsten alloy or the like. The fin plates 106, 110 are fixed tothe flow rate detector 105 and the temperature detector 109 throughjoint material such as silver paste or the like.

The flow rate detector 105 has the same construction as the flow ratedetector 5 described above with reference to FIG. 3. The temperaturecompensating measuring portion 104 has the same construction as thefluid temperature detector 9 described above with reference to FIG. 4

Various methods may be used to manufacture the flow rate sensor 101,however, the fin plate 106 and the output terminals 107, and the finplate 110 and the output terminals 111 may be respectively formed from asingle body.

For example, as shown in FIG. 20, a plate raw material 138 issuccessively etched to form plate bases 139 each having a desired shape(S1), a silver plating treatment is conducted on the portion to whichthe flow rate detector 105 will be joined (S2), silver paste is coatedto fix the flow rate detector 105, the flow rate detector 105 and eachof the output terminals 107 are connected to each other by the bodingwires 108, and then nickel plating treatment is conducted on the portioncorresponding to the fin plate 106 (S3). The flow rate detector 105, theupper half portion of the fin plate 106 and the lower half portions ofthe output terminals 107 are molded by epoxy resin to form the housing102 (S4), thereby manufacturing the flow rate sensor 101.

When the fin plate 110 and the output terminals 111 are formed from asingle body, the same process as the case where the fin plate 106 andthe output terminals 107 are formed from a single body at the same timeis carried out except that the temperature detector 109 is used in placeof the flow rate detector 105.

The flow rate sensor 101 of the present invention is used while insertedand fitted in a strainer-installed type flowmeter 140 as shown in FIGS.21 and 22. In FIGS. 21 and 22, the strainer-installed type flowmeter 140is achieved by integrating a strainer portion 142 and a flowmeterportion 143 into one body while a casing 141 is commonly used.

The casing 141 is achieved by die-casting aluminum, zinc, tin alloy orthe like. Connecting portions 144, 145 are formed at both the endportions of the casing 141 to connect the casing 141 to external pipes,and a flow-in side fluid channel 146 and a flow-out side fluid channel147 are formed in the casing 141. The strainer portion 142 comprises thelower left portion of the casing 141, a filtering member 148 and afiltering member inserting cylinder 149.

A cylinder fixing portion 150 which is slightly downwardly expanded isformed at the lower half portion of the casing 141, and a fixing recessportion 151 having a female screw portion on the inner peripheralsurface thereof is formed at the inside of the cylinder fixing portion150. An engaging projecting portion 152 is formed at the center portionof the fixing recess portion 151.

A vertical portion of the flow-in side fluid channel 146 opens upon theupper wall surface of the fixing recess portion 151, and a verticalportion of the flow-out side fluid channel 147 opens upon the lower endsurface of the engaging projecting portion 152.

The vertical portion of the flow-out side fluid channel 147 has an airpassage 153 at the upper portion thereof, a female screw portion isformed in the air passage 153, and a sealing member 154 is fastened tothe female screw portion.

The filtering member 148 comprises a holder 148 a and a filteringmaterial 148 b. The holder 148 a is achieved by die-casting aluminum,zinc, tin alloy or the like, and flange portions at both the ends of theholder 148 a are connected to each other by a cylindrical connectionportion, and a through hole 148 c is formed at the center portionthereof. Many small-diameter intercommunicating holes 148 d are formedin the cylindrical connection portion of the holder 148 a. The filteringmaterial 148 b comprises non-woven cloth of glass fiber, plastic fiberor the like, and it is mounted on the outer peripheral surface of thecylindrical connection portion of the holder 148 a.

The filtering member inserting cylinder 149 is formed by die-castingaluminum, zinc, tin alloy or the like, and a male screw portion isformed on the outer peripheral surface of the upper end portion. Thefiltering member 148 is mounted at the center portion on the bottomsurface of the filtering member inserting cylinder 149, and when themale screw portion of the filtering member inserting cylinder 149 isengaged with the female screw portion of the fixing recess portion 151to make the upper end surface of the filtering member inserting cylinder149 abut against the upper wall surface of the fixing recess portion 151through an annular thin-plate sealing member 155, the upper end openingof the through hole 148 c of the filtering member 148 is closed by theengaging projecting portion 152.

Kerosene is made to flow into the fluid channels 146, 147, and thesealing member 154 is fastened to the air passage 153 after it ischecked that no air remains in the fluid channels. When kerosene flowsthrough the flow-in side fluid channel 146 of the casing 141 and flowsinto the filtering member inserting cylinder 149, kerosene flowsdownwardly along the outer periphery of the filtering member 148, and istrapped on the bottom surface of the filtering member inserting cylinder149.

Foreign matters such as dust, dirt, etc. are removed from kerosene whilethe kerosene passes through the filtering member 148 b. The kerosenethus filtered passes through the intercommunicating holes 148 d of theholder 148 a, flows into the through hole 148 c, flows through theopening of the vertical portion of the flow-out side fluid channel 147to the flow-out side fluid channel 147, and then flows to the flowmeterportion 143. The flowmeter portion 143 comprises the upper right portionof the casing 141, the flow rate sensor 101, the sensor press plate 156,the flow rate detecting circuit board 157 and the lid 158.

As shown in FIG. 22, a recess portion on which the flow sensor ismounted is formed at the right half portion of the casing 141. Therecess portion comprises a sensor insertion space 159 and a sensorinsertion hole 160 which is formed so as to extend from the sensorinsertion space 159 to the vertical portion of the flow-out side fluidchannel 147. The lid 158 is formed by die-casting aluminum, zinc, tinalloy or the like, and it is detachably mounted on the casing 141.

The flow rate sensor 101 is engagedly inserted from the sensor insertionspace 159 of the casing 141 to the sensor insertion hole 160 so that thelower ends of the fin plates 106, 110 extend to the left side of theaxial line of the flow-out side fluid channel 147. In order to preventleakage of fluid from the gap between the flow rate sensor 101 and thesensor insertion hole 160, an O-ring 161 is interposed at the stepportion of the sensor insertion hole 160.

After the flow rate sensor 101 is fitted in the sensor insertion hole160, the sensor press plate 156 is inserted into the sensor insertionspace 159 to press the upper surface of the housing 102 of the flow ratesensor 101, and the sensor press plate 156 is fixed to the casing 141 byscrews. Further, the flow rate detecting circuit board 157 is insertedinto the sensor insertion space 159, and the lid 158 is mounted on andfixed to the casing 141, thereby fabricating the flow meter portion 143.

In the flow rate measuring portion 103 of the flow rate sensor 101, thetemperature sensor 31 is heated by supplying current to the heater 33,and variation of the electrical resistance value of the temperaturesensor 31 is detected. Here, since the flow rate sensor 101 is disposedso as to face the flow-out side fluid channel 147, a part of the heatingvalue of the heater 33 is dispersed to kerosene flowing in the flow-outside fluid channel 147 through the fin plate 106, and the heating valuetransferred to the temperature sensor 31 is equal to the value achievedby subtracting the dispersed heating value from the heating value of theheater 33. The dispersed heating value is varied in accordance with theflow rate of kerosene, and thus the flow rate of kerosene flowing in theflow-out side fluid channel 147 can be measured by detecting thevariation of the electrical resistance value of the temperature sensor31 which varies in accordance with the heating value to be suppliedthereto.

Since the dispersed heating value is also varied in accordance with thetemperature of kerosene, the temperature compensating measuring portion104 is provided in the flow rate sensor 101 to add a temperaturecompensating circuit to the flow rate detecting circuit for suppressingthe error of the flow rate measurement value due to the temperature ofkerosene at maximum.

The flow rate detecting circuit board 157 is electrically connected tothe flow rate sensor 101, the display portion 228 provided on thesurface of the casing 141 and a power supplying code, therebyconstructing an electrical circuit as shown in FIG. 23.

In FIG. 23, AC 100V serving as a power source is converted to DC voltagehaving a proper voltage value by a DC converter circuit 265. The DCvoltage thus achieved is stabilized by a voltage stabilizing circuit 266to apply the DC voltage to a heater 243 (heater 33 of FIG. 3) of theflow rate measuring portion 103 of the flow rate sensor and a bridgecircuit 267.

The bridge circuit 267 comprises a temperature sensor 247 (temperaturesensor 31 of FIG. 3) of the flow rate measuring portion 103 of the flowrate sensor, a temperature sensor 268 (temperature sensor 31′ of FIG. 4)of the temperature compensating measuring portion 104 of the flow ratesensor, a resistor 269 and a variable resistor 270. Since the electricalresistance value of the temperature sensor 247 is varied in accordancewith the flow rate of kerosene, the voltage difference (potentialdifference) Va−Vb at the points a, b of the bridge circuit 267 is alsovaried. The voltage difference Va−Vb is input to a V/F convertingcircuit 273 through a differential amplifying circuit 271 and anintegrating circuit 272, and a pulse signal having the frequencycorresponding to an input voltage signal is formed in the V/F convertingcircuit 273. The frequency of the V/F converting circuit 273 is formedon the basis of a reference frequency which is set with a high-precisionclock in a reference frequency generating circuit 275 on the basis ofoscillation of a temperature compensated type quartz oscillator 274.

When the pulse signal output from the V/F converting circuit 273 isinput to a transistor 276, current flows into the heater 243 to heat theheater 243. The pulse signal is counted by a counter 277, and the countvalue is converted to the flow rate corresponding to the frequencythereof in a microcomputer 278. The flow rate value thus achieved isdigitally displayed on the display portion 228, and also stored in amemory 279.

Reference numeral 280 represents a backup power source such as a batteryor the like.

The above circuit construction is equivalent to the circuit constructionof FIG. 9 from which the memory in the sensor unit is removed.

INDUSTRIAL UTILITY

As described above, according to the flow rate sensor unit and theflowmeter of the present invention, even when the connection statebetween the chip of each of the flow rate detector and the fluidtemperature detector and the thermal conductor or the leads is varied inaccordance with an individual flow rate sensor unit, the flow ratemeasurement can be carried out with high precision by the flow ratesensor unit concerned. Further, when the flow sensor unit is used as adisposal one, the high measurement precision can be kept.

Further, according to the present invention, even when heat flow occursbetween the inside of the housing and the outside of the housing throughthe leads, the thermal conduction between the fluid in the fluid channeland the inside of the housing through the thermal conductor can beexcellently performed, so that the effect of the heat transfer from/intothe inside of the housing through the leads can be effectively preventedfrom extending to the flow rate detector, and the flow rate measurementcan be performed stably irrespective of the external environment and thevariation thereof.

Still further, according to the flow rate sensor of the presentinvention, the flow rate measuring portion and the temperaturecompensating measuring portion are provided in one housing, so that theprocess of fabricating these measuring portions can be more simplyperformed and the manufacturing cost can be set to a lower value ascompared with a case where the measuring portions are provided todifferent housings. Particularly in the process of fixing the bondingwires for connecting the flow rate detector and the temperature detectorto the output terminals, the bonding wires can be gathered at one placeand thus the fixing work can be efficiently performed.

What is claimed is:
 1. A flow rate sensor unit in which a flow ratedetector having a heater and a flow rate detecting temperature sensor isjoined to a flow rate detecting thermal conductor, and the flow ratedetector and a part of the flow rate detecting thermal conductor areaccommodated in a housing, characterized in that said housing enclosesin a space formed therein a memory for storing individual information ofsaid flow rate sensor unit used when a flow rate value is achieved onthe basis of a detection signal of a detecting circuit containing saidheater and said flow rate detecting temperature sensor, and said flowrate detector and said memory are connected to plural leads in saidspace, said plural leads being partially exposed to the outside of saidhousing, wherein a fluid channel member having a fluid channel formedtherein is connected to or formed integrally with said housing, and saidflow rate detecting thermal conductor extends from said space into saidfluid channel.
 2. The flow rate sensor unit as claimed in claim 1,wherein a fluid temperature detector containing a fluid temperaturedetecting temperature sensor is joined to a fluid temperature detectingthermal conductor, said housing encloses in the space formed thereinsaid fluid temperature detector and a part of said fluid temperaturedetecting thermal conductor, said detecting circuit contains said fluidtemperature detecting temperature sensor, and in said space said fluidtemperature detector is connected to plural leads which are partiallyexposed to the outside of said housing, and wherein said fluidtemperature detecting thermal conductor extends from said space intosaid fluid channel.
 3. The flow rate sensor unit as claimed in claim 1,wherein the individual information stored in said memory is correctioninformation for a standard calibration curve used when the flow ratevalue is achieved on the basis of the detection signal of said detectingcircuit.
 4. A flowmeter including said flow rate sensor unit as claimedclaim 1, and an electrical circuit portion connected to the leads of theflow rate sensor unit, wherein said electrical circuit portion achievesthe fluid flow rate value on the basis of the detection signal of saiddetecting circuit by referring to a standard calibration curve stored inadvance, and at that time corrects the standard calibration curve byusing the individual information stored in said memory of said flow ratesensor unit.
 5. The flowmeter as claimed in claim 4, wherein saidelectrical circuit portion includes an analog circuit portion forachieving the output corresponding to the flow rate of the fluid byusing the detection signal of said detecting circuit, and a digitalcircuit portion for achieving the fluid flow rate value on the basis ofthe output of said analog circuit, and said digital circuit portionincludes a microcomputer and a main memory for storing the standardcalibration curve.
 6. The flowmeter as claimed in claim 5, wherein theindividual information stored in said memory of said flow rate sensorunit reflects plural relationships between the output valuecorresponding to the fluid flow rate actually-measured for said flowrate sensor unit and the true fluid flow rate value.
 7. The flowmeter asclaimed in claim 4, wherein said leads of said flow rate sensor unit andsaid electrical circuit portion are detachably connected to each other.8. A flow rate sensor unit in which a flow rate detector having a heaterand a flow rate detecting temperature sensor is joined to a flow ratedetecting thermal conductor, and the flow rate detector and a part ofthe flow rate detecting thermal conductor are accommodated in a housing,characterized in that a fluid channel member having a fluid channelformed therein is connected to or formed integrally with said housinghaving a space formed therein, said flow rate detecting thermalconductor extends from said space into said fluid channel, a thermalconductor other than said flow rate detecting thermal conductor isdisposed so as to extend from said space into said fluid channel, saidhousing encloses in the space formed therein a memory for storingindividual information of said flow rate sensor unit used when a flowrate value is achieved on the basis of a detection signal of a detectingcircuit containing said heater and said flow rate detecting temperaturesensor, and said flow rate detector and said memory are connected toplural leads in said space, said plural leads being partially exposed tothe outside of said housing.
 9. The flow rate sensor unit as claimed inclaim 8, wherein a fluid temperature detector containing a fluidtemperature detecting temperature sensor is joined to a fluidtemperature detecting thermal conductor, said housing encloses in thespace formed therein said fluid temperature detector and a part of saidfluid temperature detecting thermal conductor, said fluid temperaturedetecting thermal conductor extends from said space into said fluidchannel, said detecting circuit contains said fluid temperaturedetecting temperature sensor, and in said space said fluid temperaturedetector is connected to plural leads which are partially exposed to theoutside of said housing.
 10. The flow rate sensor unit as claimed inclaim 8, wherein the individual information stored in said memory iscorrection information for a standard calibration curve used when theflow rate value is achieved by using the detection signal of saiddetecting circuit.
 11. The flow rate sensor unit as claimed in claim 8,wherein said thermal conductor extends to be nearer to the portions ofsaid leads in said housing than said flow rate detecting thermalconductor.
 12. The flow rate sensor unit as claimed in claim 9, whereinsaid thermal conductor extends to be nearer to the portions of saidleads in said housing than said fluid temperature detecting thermalconductor.
 13. The flow rate sensor unit as claimed in claim 8, whereinsaid memory is joined to said thermal conductor.
 14. The flow ratesensor unit as claimed in claim 9, wherein said flow rate detectingthermal conductor, said fluid temperature detecting thermal conductorand said thermal conductor are designed in a plate shape, and arrangedalong the direction of said fluid channel on the same plane in saidfluid channel.
 15. A flowmeter containing said flow rate sensor unit asclaimed in claim 8, and an electrical circuit portion connected to theleads of said flow rate sensor unit, wherein said electrical circuitportion achieves the fluid flow rate value on the basis of the detectionsignal of said detecting circuit by referring to a standard calibrationcurve stored in advance, and at that time corrects the standardcalibration curve by using the individual information stored in saidmemory of said flow rate sensor unit.
 16. The flowmeter as claimed inclaim 15, wherein said electrical circuit portion includes an analogcircuit portion for achieving the output corresponding to the flow rateof the fluid by using the detection signal of said detecting circuit,and a digital circuit portion for achieving the fluid flow rate value onthe basis of the output of said analog circuit, and said digital circuitportion includes a microcomputer and a main memory for storing thestandard calibration curve.
 17. The flowmeter as claimed in claim 16,wherein the individual information stored in said memory of said flowrate sensor unit reflects plural relationships between the output valuecorresponding to the fluid flow rate actually-measured for said flowrate sensor unit and the true fluid flow rate value.
 18. The flowmeteras claimed in claim 15, wherein said leads of said flow rate sensor unitand said electrical circuit portion are detachably connected to eachother.
 19. A flow rate sensor comprising a flow rate measuring portionfor detecting the flow rate of fluid, a temperature compensatingmeasuring portion for compensating an effect of fluid temperature onmeasurements of said flow rate measuring portion, and a housing, whereinsaid flow rate measuring portion includes a flow rate detector having aheater and a temperature sensor laminated each other through aninsulator, a fin plate joined to the flow rate detector at one endthereof, and an output terminal electrically connected to the flow ratedetector, said temperature compensating measuring portion includes atemperature detector having an insulator and a temperature sensor thatare laminated on each other, a fin plate joined to said temperaturedetector at one end thereof, and an output terminal electricallyconnected to said temperature detector, said housing encloses said flowrate detector and said temperature detector therein, and said fin platesand the output terminals of said flow rate measuring portion and saidtemperature compensating measuring portion are projected to the outsideof said housing.
 20. The flow rate sensor as claimed in claim 19,wherein said housing is formed of synthetic resin having thermalconductivity of 0.7 w/m·K or less.
 21. The flow rate sensor as claimedin claim 19, wherein a cavity portion is provided in said housing, andsaid flow rate detector and said temperature detector are mounted at aposition of the cavity portion at which said flow rate detector and saidtemperature detector are not brought into contact with said housing.